How to copy one register to another?

Question

In vim :let @"=@* will copy the content of* register to the " register. How can it be done with evil?

Answer 1

This code should do that.

(set-register ?" (get-register ?*))

If you want that in a command:

(defun foo ()
  (interactive)
  (set-register ?" (get-register ?*)))

Or if you want a command that reads the register names:

(defun copy-register-to-register (from to)
  (interactive
   (list (register-read-with-preview "From register: ")
         (register-read-with-preview "To register: ")))
  (set-register to (get-register from)))

(Emacs registers are not particular to Evil, so Evil is, I think irrelevant to your question. Evil may be how you interact with registers, but setting them with Elisp should independent of Evil.)

Answer 2

(evil-set-register ?\" (evil-get-register ?*))